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A gas turbine engine exhaust nozzle arrangement for the flow of exhaust gases therethrough between an upstream end and a downstream end thereof comprising a nozzle and a plurality of tabs which extend in a generally axial direction from a downstream portion of the nozzle wherein the nozzle further c

A gas turbine engine exhaust nozzle arrangement for the flow of exhaust gases therethrough between an upstream end and a downstream end thereof comprising a nozzle and a plurality of tabs which extend in a generally axial direction from a downstream portion of the nozzle wherein the nozzle further comprises an actuation mechanism capable of moving the tabs between a first deployed position, where the tabs interact with a gas stream to reduce exhaust noise thereof, and a second non-deployed position, where the tabs are substantially aerodynamically unobtrusive.

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We claim: 1. A gas turbine engine exhaust nozzle arrangement for the flow of exhaust gases therethrough between an upstream end and a downstream end thereof comprising a nozzle, a downstream portion and a plurality of tabs, each tab extending in a generally axial direction from the downstream porti

We claim: 1. A gas turbine engine exhaust nozzle arrangement for the flow of exhaust gases therethrough between an upstream end and a downstream end thereof comprising a nozzle, a downstream portion and a plurality of tabs, each tab extending in a generally axial direction from the downstream portion of the nozzle wherein the nozzle further comprises an actuation mechanism capable of moving the tabs between a first deployed position, with in the first position the tabs interacting with a gas stream to reduce exhaust noise thereof, and a second non-deployed position, in the second position the tabs being substantially aerodynamically unobtrusive, said tabs being made of a material that upon exposure to an elevated temperature causes the material to assume a position to place said tabs in said first position and to move the tabs to said second respective position upon the absence or reduction of the temperature. 2. A gas turbine engine exhaust nozzle arrangement as claimed in claim 1 wherein the plurality of tabs is circumferentially disposed about the nozzle. 3. A gas turbine engine exhaust nozzle arrangement as claimed in claim 1 wherein the actuation mechanism comprises a shape memory material element. 4. A gas turbine engine exhaust nozzle arrangement as claimed in claim 3, the nozzle further comprises a radially inner position and a radially outer part, wherein the tabs are rotatably attached to the nozzle at the radially inner position, the actuation mechanism comprises the shape memory element mounted at a first end to a radially outer part of the nozzle and mounted at a distal end to a radially outer part of the tab, such that in use, the element in a first shape maintains the tab in the second non-deployed position and in a second shape maintains the tab in the first deployed position. 5. A gas turbine engine exhaust nozzle arrangement as claimed in claim 3 wherein the periphery of the nozzle defines a pocket therein and at least a part of the element is generally disposed within the pocket. 6. A gas turbine engine exhaust nozzle arrangement as claimed in claim 3 wherein the tab defines a recess therein and at least a part of the element is generally disposed within the recess. 7. A gas turbine engine exhaust nozzle arrangement as claimed in claim 3 wherein the element is in the form of a spring. 8. A gas turbine engine exhaust nozzle arrangement as claimed in claim 1 wherein the nozzle arrangement comprises a resilient member having a first end and a distal end, the resilient member is attached at the first end to the tab and at the distal end to the nozzle and is arranged to provide a returning force to the tab. 9. A gas turbine engine exhaust nozzle arrangement as claimed in claim 5 wherein the nozzle defines an orifice and a passage, the orifice is exposed to a gas stream and the passage extends from the orifice to the pocket and thereby provides a conduit for transmitting the thermal flux of the gas stream to the actuation mechanism. 10. A gas turbine engine exhaust nozzle arrangement as claimed in claim 1 wherein the tab comprises shape memory material. 11. A gas turbine engine exhaust nozzle arrangement as claimed in claim 10 wherein the tab further comprises a flexural element, the flexural element, in use, is arranged to provide a returning force to the tab. 12. A gas turbine engine exhaust nozzle arrangement as claimed in claim 10 wherein the tab defines an orifice, the orifice exposed to a gas stream, and a passage, the passage extending from the orifice, to the shape memory material and thereby provides a conduit for rapidly transmitting changes in the thermal flux of the gas stream to and throughout the memory shape material element. 13. A gas turbine engine exhaust nozzle arrangement as claimed in claim 1 wherein the actuation mechanism is actuated in a response to an applied field. 14. A gas turbine engine exhaust nozzle arrangement as claimed in claim 13 wherein the field is a temperature flux. 15. A gas turbine engine exhaust nozzle arrangement as claimed in claim 13 wherein the field is an electric current. 16. A gas turbine engine exhaust nozzle arrangement as claimed in claim 13 wherein the temperature flux is provided by the gas stream and the gas stream is any one chosen from the group comprising an ambient gas flow, a bypass flow, a core flow. 17. A gas turbine engine exhaust nozzle arrangement as claimed in claim 2 wherein the shape memory material element comprises any one of a group comprising Titanium, Manganese, Iron, Aluminium, Silicon, Nickel, Copper, Zinc, Silver, Cadmium, Indium, Tin, Lead, Thallium, Platinum. 18. A gas turbine engine exhaust nozzle arrangement as claimed in claim 2 wherein the shape memory material element comprises an electrostrictive material. 19. A gas turbine engine exhaust nozzle arrangement as claimed in claim 18 wherein the actuation mechanism further comprises an electrical circuit, the electrical circuit comprising control apparatus, an electric generating means and electrical contact means, the electrical contact means arranged to deliver, in use, an electrical signal, generated by the electrical generating means, through the electrostrictive material, the control apparatus operable to control the electrical signal. 20. A gas turbine engine exhaust nozzle arrangement as claimed in claim 19 wherein when the control apparatus is operated to deliver the electrical signal to the electrostrictive material, thereby actuating the electrostrictive material, the tab is moved from a second non-deployed position and a first deployed position and when the control means is operated so as not to deliver the electrical signal the electrostrictive material moves the tab between the first deployed position and the second non-deployed position.